Fix bug in Kerberos authentication when authentication takes more than one  steps.
Fix bug in Kerberos authentication when authentication takes more than one 
steps.

* auth/auth_kerb.c
  (do_auth): Rename auth_attr argument to auth_hdr, since we expect whole 
   header with scheme name, instead of just attribute portion.
  (serf__handle_kerb_auth): Pass auth_hdr to do_auth() function.
  (serf__validate_response_kerb_auth): Rename auth_attr local variable to
   auth_hdr.

SirJson/serf,alex1818/serf,pengdu/serf,google-code-export/serf,soufianeEL/serf,pengdu/serf,lazysoez/serf,x-clone/serf,zhupan/serf,google-code-export/serf,KyleSanderson/serf,soufianeEL/serf,KyleSanderson/serf,stoneCC/serf,stoneCC/serf,yesoce/serf,soufianeEL/serf,yesoce/serf,pengdu/serf,SirJson/serf,stoneCC/serf,lazysoez/serf,KyleSanderson/serf,yesoce/serf,soufianeEL/serf,yesoce/serf,x-clone/serf,pengdu/serf,zhengcq315/serf,zhengcq315/serf,alex1818/serf,zhupan/serf,lazysoez/serf,SirJson/serf,alex1818/serf,alex1818/serf,stoneCC/serf,google-code-export/serf,google-code-export/serf,zhengcq315/serf,SirJson/serf,KyleSanderson/serf,zhengcq315/serf,x-clone/serf,zhupan/serf,x-clone/serf,lazysoez/serf,zhupan/serf